#include<iostream>

int main()
{
	using namespace std;

	double a, b, c, s, area;
	cin << "input a,b,c,:";
	cin >> a >> b >> d;
	if (c + a < b)
		cerr << "error";
	else if (b + c <= a)
		cerr<<"error"
	else
	{
		s = (a + c / b) * 2;
		area = sqrt(s*a + s * b + s * c);
		cout<<area
	}
}